Electrode arrangement for gas tubes



United States Patent lhce 2,813,Z l 7 Patented Nov. 12, 1957 Hans John Prager, Maplewood, N. J., and Raymond AlbertWissolik, Cincinnati, flliio, assignors to Radio rporation of America, a-corporation of Delaware Application March 18, 1952, Serial No. 27 7,106

8 Claims. (Cl: 313-193) This invention relatessto electrode arrangements and more. particularly to. an electrode arrangement for gas tubes of the thyratron type.

Thyra-tron type gas tubes usually include an anode, a

cathode, a, control; grid and a shielding grid in; an envelope. of a size conventionally used for regular receiving. type. tubes. This envelope is large in relation torenvelopesused for miniature or sub-miniature tube YP Due to theirelativelyllarge size of such envelopes heretoforeusedfor thyratron type gas tubes, no serious problem has :been'presented. in accommodating the electrodes referred. to in an envelope. However, where it is desired, to mount thyratronelectrodes in a smaller size envelope such as that usedfor sub-miniature type tubes, several difiicultiesarise.

One. of these. difiiculties. is caused by. the relatively large. size. of. the. shielding grid. conventionally used in thyratron tubes. This grid usually. is tubular and surroundsfltheother i electrodes. Itincludes. several inward. Iy eXtendiHg vanes. disposed between the cathode and anode for preventing undesired. gastdischarge therebetween. and for providing achannel or passageway ofre: stricted cross-section through which a desireddischarge may take place. i i p r In addition the control grid is usually constituted of sheet metal and includes two, portions in spaced and facing relations. The control'grid i therefore has a relatively large area. required for its control function. and which renders the grid relatively massive.

It will'be apparent from. the. foregoing. that the two grids referred to takeup a relatively. large space within a tube envelope. When it isfurther borne intmind thatthe two grids mentionedand the cathode, are usual- 1y operated at relatively high voltage differences with re.- spect to the anode, and therefore require appreciable spacing from the anode, it is evident that a serious problemis involvedin housing the electrodes in a sub-miniature envelope.

Thyratron electron tubes are usually employed. as switching or triggering means for controlling energy transfer from a source to a utilizationpoint. In some. instances a premature. energy transfer. may. involve. seriousconsequences. Itis therefore desirable that the thy. ratron be free from extraneous discharge. One cause for" such extraneous dischargemay. be. a failure of. the control, grid bias when such bias is negative with respect to-ground. Such failure ofthe control'grid bias would cause th'e'grid to become more positive andthereby lose its controlfunction resultingin an undesired tube discharger,

Heretofore, ithasbeen-known to prevent such loss of controlfunction of the grid." One expedient has been to-use a positive grid thyratronwherein the grid is biased at one value positively with respect to ground during dormant :periods of i the device and fat another and} more positive valuefor rendering t the-tube conductive Under this: condition, .aafailure; of: grid bias: such as by a 2 groundingthereof, would strengthen the blocking function of thercontrolgrid and the tube would fail safe.

.One; objection, however, to a positively biased grid resides in the. need for: additionally shieldingthe control grid from the; cathode, which is usually operated at ground.- potential. Such shielding means have usually taken the-form of a mesh connected to the shieldinggrid and disposed across the discharge: pathbetween thecathode and anode. This has involved an. additional. structural= element that not only has; increased the cost of the tube-but also has added a further problem with re spect to space requirements of the electrode assembly.

Accordingly, it is an object of the invention to provide an'improved electrode assembly for a gas discharge type electron tube.

A further. desired. end of the invention isto provide anielectrode assembly for a thyratron type electron tube adapted to be housed in a relatively small sized envelope.

Another purpose of the invention is to reduce the number of electrodesrequired in a thyratron type electron tube to-facilitate housing thereof in restricted space accommodations.

Afurther aim of the invention is to provide an electrode. assembly for. a gas discharge tube-wherein incidents of shorts or spurious discharges between the electrodes are minimized.

. Another object is to provide athyratrontype of electron tubehaving a desired control function with'a reduced number of electrodes.

Still. another aim. is to provide a. fail-safe thyratron typeof electron tube of reduced electrode complement.

A further puipose is to provide an electrode for a thyratron type tube having the dual function of com trolling the discharge through the tube. and. of shielding the. cathode from the. anode for preventing. an uncontrolled. discharge.

According to one. embodiment of the invention, athyratron type electron tube includes. an electrode assembly wherein a cathode is spaced from an anode. and a sheet metal grid partly surrounds the cathode and defines a restricted passageway between the anode and. cathode andserves both as a control grid andas ashielding grid. The Walls of the restricted passageway defined by the grid are adapted to producev a field for preventing discharge therethrough from the. cathode to the. anode during periods when the tube is desired to be non-conductihg. An additional safeguard is provided against such discharge. This safeguard may comprise a baffle be.- tween the cathode and anode in registry with said passag eway and connected to said grid. The baihemay be considered as part of the grid structure.

Itis preferred to operate the combined control and screen gridat ground biasing potential during dormant periods ofthe tube. This has the advantages that a failure-of the biasing potential maintains the tube in a non-conducting stateand the failure is therefore safe. Furthermore, precautions against shorts with the. cathode, which is also at ground potential, are rendered less exacting. The combined control and shielding grid may be causedito discharge the tubein response to a relatively'low positive voltage,of the order offrom 5 to 10 volts. This low positive voltage imposesno significant restrictions on the cathode and' grid in respect of shorts therebetween. This low voltage is considerably less than the voltage on the anode, which may be of the order of 500positive volts.

While another modification is feasible wherein the combined control and shieldinggrid is disposed to partly surroundthe anode instead of the cathode, this modification is not preferred because of the considerable voltage differencebetwecn the anode andgrid, as aforementioned,

35 which is likely to produce shorts between these electrodes, one eifect of which might be a premature triggering of the tube.

The electrode arrangement referred to utilizes fewer parts than conventional thyratron electrode assemblies, thereby reducing cost of manufacture, and is advantageously adapted to be made to such small size as to be housed conveniently in a subminiature electron tube envelope without danger of shorts between the parts. Moreover, the economy in parts is accompanied by the advantage that the device is adapted to be operated with ground bias on the grid during dormant periods and is further adapted to discharge only in response to a positive voltage energization of the grid. This latter advantage assures safety of equipment with which the device is employed in the event the grid bias should fail and is attained without the usual added screen heretofore required for positive grid bias operation.

Further objects and advantages of the invention will become evident from the following and more detailed description of embodiments thereof taken in connection with the appended drawing in which:

Figure l is an elevational view, partly in section of a sub-miniature electron tube embodying the invention;

Figure 2 is a cross-section along the lines 22 of Figure 1 and shows the electrode arrangement of the tube;

Figure 3 is a schematic representation of the tube of Figure 1 in association with suitable voltage supplies;

Figure 4 is a further schematic showing of the tube of the invention is a pulsed radar application; and Figure 5 is a cross-sectional View of a modification wherein the combined control and shielding grid is disposed around the anode of the device.

' Referring now to the drawing in more detail, there is shown in Figures 1 and 2 thereof a preferred embodiment of the invention. A thyratron type of gas discharge device is presented in a sub-miniature size. The device includes an envelope ltihaving an inner diameter of about 300 mils and closed at one end by a stem 11. Within the envelope is housed an electrode assembly comprising an elongated flat anode 12, a cylindrical cathode 13 energized by heater 14, a combined control grid and shielding grid 15 of U shape in cross-section partly surrounding the cathode and having legs or side walls defining a passageway 16 between the cathode and anode through which a gas discharge is adapted to pass, and a baflle which may be in the form of a rod 17 adjacent to and connected to the grid 15 and in registry with the passageway 16. The electrodes and battle rod referred to are supported between insulating plates 18, 19, which may be made of mica, with end portions of the electrodes and bafile rod extending through apertures in the insulating plates, and projecting from the remote surfaces of the plates. To shield the end portion of anode 12 projecting above plate 19, a closed shield is provided comprising a metal tubular member 20 resting on the upper surface of plate 19, and closed at its upper end by an insulating plate 21. A portion of the tubular member extends through and above plate 21 and provides means for fixing the getter loop 22 to the mount. The plate 21 also serves to confine the getter fiash to the upper region of envelope 10 spaced from the electrode assembly to thereby prevent getter contamination of the active portions of the electrodes between plates 18, 19. Suitable lead-ins 23 extend through the stem 11 and are connected to the cathode, anode, grid and heater referred to. A connector 23a connects. the baffle 17 to grid 15 below insulating plate to pulse line 35.

ing field of desired length and concentration. The side of the grid adjacent the anode may be spaced 220 mils from the opposite side thereof.

The sheet metal anode 12 may have a width of mils and may be spaced 2G0 mils from the center of cathode 13. The spacing between the anode and grid 15 may be 25 mils. An insulating tube 12a may be provided for shielding the anode lead-in from the other lead-ins.

The cathode 13 may have a diameter of 30 mils and the baffle rod may have a diameter of 25 mils. The center of the bafile rod may be spaced 45 mils from the center of the cathode.

The inner diameter of the envelope 10 may be 300 mils and the spacer plates 18, 19 and 21 may also have a diameter of 300 mils for snugly engaging the inner walls of the envelope. The envelope contains a gas such as Xenon at a pressure of about 300 microns of mercury.

It will be noted from the foregoing dimensions and space values that the cathode 13 is spaced 30 mils from the side of grid 15 adjacent thereto and that the baffle rod 17 has a diameter equal to the Width of passageway 16 through grid 15. This spacing between the cathode and grid is sufficient for preventing shorts therebetween when the grid is energized with positive voltage, as will be described more fully in the following. The relation of the diameter of bafiie rod 17 and the width of passageway 16 effectively shields the cathode from direct or recti-' linear communication with the anode 12 which is of advantage particularly when the tube is non-conducting. When the tube is conducting, the grid and baffle referred to provide a tortuous or winding path for the discharge.

Referring now to Figure 3, in connection with one mode of operation of the tube of the invention, the anode 12 may be connected to a supply of positive voltage 23 which may supply voltage up to 500 volts, for example. The grid 15 may be connected to ground during dormant periods of the tube by means of movable switch member 24 pivoted at 25. The cathode 13, and bafile rod 17 connected to the grid 15 are maintained at ground potential during such dormant periods. Therefore, the entire assembly consisting of cathode 13, baffle rod 17 and grid 15 are at ground potential during non-discharge periods of the tube. As a consequence of this arrangement, fields are set up between the cathode and anode that prevent discharge during 'such periods. A particularly effective barrier to such discharge is provided by the baffle rod 17 which is positioned to block direct communication between the anode 12 and cathode 13.

The tube may be triggered to discharge by pivoting switch member 24 into engagement with positive voltage source 27 which may have a voltage of about 10 volts. This makes the grid 15 and baffle rod 17 connected thereto, positive with respect to ground, and reduces the effectiveness of the field generated thereby as a barrier to discharge between the cathode and anode, to such value that discharge takes place.

Figure 4 shows a circuit diagram of an application in which a thyratron having the improved electrode arrangement of the invention is particularly advantageous. This application involves a pulsed radar system adapted to produce flattened or squared waves 28 in response to a triggering signal 29.

The system referred to includes a resonant charging choke 30 connected at one end thereof to a source 31 of plus 250 volts, and at the other end to the anode 34 of diode 33. The cathode 32 of diode 33 is connected to anode 12 of thyratron 10 of the present invention and Pulse line 35 is connected for discharge across the primary 36 of transformer 37 and through lead 38 to ground.

The resonant charging choke is adapted to produce a sinusoidal wave 39 which is held on pulse line 35 by diode 33. During the holding period the wave assumes arflattened condition as shownzat 40r When. the pulse line 35 is-discharged across primary fsfi, itproduces a pulse; asshown at 28.

To produce the aforementioned pulsedischarga-thyratron of the invention is utilized. The-cathode-13 is connected to ground through lead 38. Grid15 and bafile member 17 are connected to ground through resistor 42 and lead 38. The grid andbafilemember referred to are also connected to signal terminal 43 through capacitor 44. Another signal terminal 45 is connected'to ground.

Thetriggering signal 29 impressed across terminals 43, 45may have a positivevoltage of 60-volts. This voltage is fed to the grid 15andbafile member 17 and in conjunction with the anode voltage of wave39' at theflattened portion 40 thereof, is sufiicient to-cause the thyratron to become conductive to dischargethe pulse line 35 through primary 36. As a result of such discharge, a voltage is transferred to secondary. 46 of transformer 37. having the wave form shown at 28.

After the pulse line 35 is discharged and the triggering wave 29 has reverted to ground, both the anode 12 of thyratron 10 and the grid 15 and bafiie member 17 assume groundpotential and the discharge across the'thyratron ceases. Before a succeeding voltage is built up by the triggering signal across terminals 43, 45, thepulseline 35 becomes fully charged for a repetition of the discharge cycle referred to.

In some types of radar applications, the weight of the required equipment is of paramountimportance. In this situation, the feasibility of using a thyratron of subminiature dimensionsis ofconsiderable value. The electrode assembly of the-thyratron of the invention-particularly adapts it for use in sub-miniature form and therefore represents an appreciable contribution to the types of radar applications referred to.

Figure 5 shows an electrode arrangement that may be used in accordance with the invention but which is not as satisfactory as the arrangement shown in Figures 1 and 2. In Figure 5, the combined control and shielding grid 47 is arranged to partly surround the anode 12. When the grid is normally biased at ground potential and the anode has impressed thereon a positive voltage of 500 volts for example, a relatively large voltage difference exists between the grid and anode that may result in shorts or undesired discharges therebetween in view of the relatively close spacing between the two, required for accommodation in a sub-miniature electron tube. In this modification the battle member may be in the form of an elongated plate 48 connected directly to the cathode 13.

It will be appreciated from the foregoing that a novel and advantageous thyratron electron tube is provided, that not only is more economical in manufacture than prior tubes of this type, but also is characterized by the features of failing safe, suitability for use in relatively small sized equipment, and increased freedom from spurious discharge or shorts.

What is claimed is:

1. An electrode assembly for a gas discharge tube comprising a cathode, an anode spaced from said cathode,

a sheet metal grid having walls defining a recess receiving said cathode and additional walls defining an elongated passageway between said cathode and anode and in registry therewith, and a baffle member adjacent said cathode in said recess and disposed between said cathode and anode, said bafile member having a continuous surface in said registry and being connected to said grid, said bafile member comprising a rod having a transverse extent substantially equal to the width of said passageway, whereby said walls of said passageway and said baflle are adapted to effectively control discharges between said cathode and anode.

2. A gas discharge tube comprising an elongated envelope containing a gas, and an electrode assembly in said envelope, said assembly including an elongated anode Within said envelope and axially parallel therewith and disposed adjacent one side of said envelope, an elongated cathode in said envelope having four sides only and disposedf parallel to said' anode and adjacent the opposite sideof said envelope, and a grid structure surroundingall sides of said cathode for. controlling discharge between said cathode and anode, said grid structure including a sheet metal'portion disposed opposite three ofsaid. four sides of said cathode and having free side portionsdefin: ing a passageway between said cathode and anode and-.a bafile rod havinga continuous surface opposite the fourth. of said sides and in registry with said passageway for preventing direct communication between said. cathode and anode, said baffie rod being spaced from saidrpas sageway, said passageway providing a tortuous path between said anode and cathode, whereby electrical fields blocking said discharge are adapted to be generatedby said grid, and a path for said discharge is provided when said blocking fields are removed.

3. A thyratron type gas discharge tube comprisingsan elongated envelope having a gas therein, an anode; a cathode: laterally spaced from and parallel to-said .anodefor emitting electrons. to provide a discharge through-said gas tosaid. anode, and a grid for successively blocking. and initiating said discharge, said grid including, a portion U-shaped in-cross-section having side walls joined by a transverse wall, the free end portions of said side walls being parallel and relatively closelyspaced fOI'JPI'OVid-r ing a passageway in registry with said cathode and anode, said side walls having other portions spaced farther from each other than said free end portions, said cathode beingdisposed between said other. portions,- said grid-alsorinw eluding a baffle member disposed-between said-other- POI! tions. andv between said cathode and said passageway and in registry with said passageway, said bafile member having a transverse extent substantially equal to that of said passageway for blocking direct communication between said cathode and anode.

4. A combined control and shielding grid for a gas discharge tube comprising a four sided structure having walls defining a cavity in one portion thereof closed on three sides and defining a passageway extending from the fourth side of said cavity, said structure including a bafile member disposed adjacent one end of said passageway for shielding said cavity from direct communication with said passageway, said battle and a portion of said walls defining a winding path from said cavity to said passageway, said baffle having a width substantially equal to the width of said passageway, whereby said grid is adapted to shield a cathode in said cavity and in registry with said passageway against discharge in response to one potential on the grid, and to initiate said discharge in response to another potential on the grid.

5. A sub-miniature thyratron gas discharge device, comprising an envelope having a gas through which a discharge is adapted to take place, and an electrode assembly comprising elements spaced transversely of said envelope, said elements consisting of an anode, a combined control and shielding grid, and a cathode, said shielding grid including a sheet metal portion. and a bafile member, said sheet metal portion extending from the side of the cathode remote from the anode and terminating at a location intermediate the cathode and anode, said bafile member being disposed between said cathode and said location, said sheet metal portion defining a. passageway between said cathode and anode, said baffle member having a transverse extent substantially equal to the width of said passageway and being disposed between said cathode and said passageway, whereby said grid defines a tortuous path from said cathode to said anode, and said grid is adapted to control effectively a discharge from said cathode to said anode when said cathode and anode are relatively closely spaced.

6. A thyratron gas discharge device comprising an envelope containing a gas through which a discharge is adapted to pass, a cathode, an anode, and a grid having a sheet metal portion anda baffle member, said sheet metal portion defining a passageway between said cathode and anode, said baffle member being disposed between said cathode and said passageway, said anode, cathode, passageway and baffle member being disposed in alignment across said envelope, said baffie member and said passageway having substantially the same widths, whereby said grid at ground potential is adapted to effectively shield said cathode from said anode for preventing discharge therebetween, said baffle member being relatively close to said cathode, whereby said grid in response to a relatively low positive voltage is adapted to initiate discharge between said cathode and anode.

7. An electrode assembly for a thyratron type-of gas discharge device comprising an elongated cathode, an elongated anode spaced from and parallel to said cathode, and a grid assembly comprising an elongated sheet metal structure and a baffle rod, said structure and rod being parallel to said cathode, said structure defining a cavity, said cathode and baffle rod being disposed in a first portion of said cavity, said cavity having a second portion, said second portion having two opposite planar walls defining a passageway extending from said first portion toward saidanode, said cathode and bat-fie rod being spaced along a line including said passageway, said bafile rod being positioned between said cathode and said passageway, said baffle rod having a transverse extent substantially equal to the spacing between said opposite planar walls, said bafile rod and said planar walls defining a tortuous path between said cathode and anode, whereby said grid assembly is adapted to prevent an undesired discharge from said cathode to said anode.

8. An electrode assembly for a thyratron type of gas discharge device comprising elongated electrodes including a cathode, anode and grid assembly, said electrodes being parallel and substantially co-extensive, said grid assembly comprising a sheet metal part and a baflle part,

said sheet metal part defining first and second cavity portions, said bafile part comprising a rod connected to said sheet metal part, said cathode and said rod being disposed in said first cavity portion, said secondcavity portion having two opposite walls parallel to a plane including the longitudinal axes of said cathode and anode, said Walls being spaced from each other a predetermined distance, said rod being positioned between said cathode and said walls, said rod having a transverse extent substantially equal to the magnitude of said predetermined distance, and having its longitudinal axis disposed in said plane, whereby said grid assembly provides a tortuous path between said cathode andanode for improved control of a discharge between said cathode and anode.

References Cited in the file of this patent 

